Calculate voltage lost across resistance from current flow
Current I (A)
Resistance R (ohm)
Source voltage (V)
Result
Answer
Step-by-Step Derivation
Voltage Drop Formula
Vdrop = I R
Vload = Vsource - Vdrop
Voltage drop follows Ohm law. When current flows through wire or any series resistance, part of the source voltage is lost before the load.
⚠For long cable runs, include both supply and return conductor resistance. Actual allowable drop depends on the device and electrical standard.
What Is Voltage Drop?
Voltage drop is the reduction in voltage caused by current flowing through resistance. It matters in real wiring because no conductor is perfectly ideal.
Ohm Law Basis
Drop equals current times resistance.
Load Voltage
Device voltage is source voltage minus drop.
Power Loss
The lost voltage corresponds to heat in resistance.
Design Check
Lower resistance or current reduces voltage drop.
Example: For I = 2 A and R = 0.5 ohm, Vdrop = 2 x 0.5 = 1 V, so a 12 V source leaves about 11 V at the load.
Applications of Voltage Drop
Cable SizingDC CircuitsAutomotive WiringLED StripsPower Distribution
Frequently Asked Questions
What is a voltage drop calculator?▼
It calculates the voltage lost across a resistance when current flows through it.
What is the voltage drop formula?▼
Voltage drop is Vdrop = I x R, where I is current and R is resistance.
How do I use this voltage drop tool?▼
Enter current, resistance, and source voltage. The tool returns drop voltage and estimated load voltage.
Why is voltage drop important?▼
Too much voltage drop can reduce device performance, waste power, and cause heating in wires.
Where is voltage drop calculation used?▼
It is used in cable sizing, DC circuits, automotive wiring, LED strips, and power distribution.
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